Not Just a Dot: The Complex UV Morphology and Underlying Properties of Little Red Dots

Journal article

We analyze 99 photometrically selected Little Red Dots (LRDs) at z ≈ 4–8 in the GOODS fields, leveraging ultradeep JADES NIRCam short-wavelength (SW) data. Among the 99 selected LRDs, we examine the morphology of 30. The remaining 69 appear predominantly compact, with sizes ≲400 pc and no extended components even in stacked SW images. However, their unresolved nature may partly reflect current depth limitations, which could prevent the detection of faint diffuse components. Among the 30 morphologically analyzed LRDs, 50% show multiple associated components, while the rest exhibit highly asymmetric structures, despite appearing as single sources. This diversity in rest-frame UV morphologies may point to interactions or strong internal feedback. We find median stellar masses of log10(M⋆/M⊙)=9.07−0.08+0.11 for pure stellar models with AV≈1.16−0.21+0.11 mag, and log10(M⋆/M⊙)=9.67−0.27+0.17 for models including active galactic nuclei (AGNs) with AV≈2.74−0.71+0.55 mag, in line with recent studies suggesting higher masses and dust content for AGN-fitted LRDs. NIRSpec spectra are available for 15 sources, six of which are also in the morphological sample. Broad Hα is detected in 40% (FWHM = 1200–2900 km s−1), and one source shows broad Hβ emission. Emission line ratios indicate a composite nature, consistent with both AGN and stellar processes. Altogether, these results suggest that LRDs are a mixed population, and their rest-frame UV morphology reflects this complexity. Morphological studies of larger samples could provide a new way to understand what drives their properties and evolution.

Authors: Rinaldi, P; Bonaventura, N; Rieke, GH; Alberts, S; Caputi, KI

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Astronomical Society
• Journal: The Astrophysical Journal
• Volume: 992
• Issue: 1
• Article number: 71
• Publication date: 2025-10-06
• Acceptance date: 2025-08-03
• DOI: 10.3847/1538-4357/adfa10
• EISSN: 1538-4357
• ISSN: 0004637X and 0004-637X
• Language: English
• Keywords: Galaxy evolution; James Webb Space Telescope; Active galactic nuclei; Near infrared astronomy; Galaxy formation